Design considerations for secure SIM-based user registration and OTP verification systems

[proseo2050]

I’m studying different approaches used in large-scale user registration systems that rely on mobile numbers for identity verification.

In particular, I’m interested in how systems handle SIM-based registration and OTP verification at scale while maintaining security and reliability.

Some key areas I’m exploring:

How to reduce OTP delivery failures across different regions and carriers
Methods to prevent SIM swap and number spoofing attacks
Rate limiting strategies for OTP requests in high-traffic systems
Balancing user experience with strict verification security
Integration patterns with telecom or SMS gateway APIs in distributed systems

If anyone has experience building or scaling such systems, I’d appreciate insights on architecture decisions, common pitfalls, and security best practices.